Currently, when a data frame is transmitted between a Mobile Station (MS) and a Base Transceiver Station (BTS), a rate determination algorithm running in the BTS determines the frame rate and whether the frame is usable or corrupted. The rate determination algorithm relies on the outcome of a traffic frame cyclic redundancy check (CRC) (also referred to as an outer CRC), SER/Total Metric and Quality bits. The actual payload of the frame itself is not considered in the rate determination process. All signaling messages contain a sixteen (16) bit CRC value (inner CRC) which is a stronger CRC than the outer CRCs used (typically 12, 10 and 8 bits). Currently, the inner CRC is not considered in determining whether the frame is corrupted. Signaling messages are usually in the form of dim and burst (partially voice, partially signaling) when transmitted on the fundamental channel. The signaling message with its 16 bit CRC is usually a small portion of the frame on the reverse link. If the bit errors that cause the rate determination algorithm to declare an erasure are not in the signaling portion of the message, the signaling portion of the frame can be recovered from the otherwise erased frame. However, currently when bits errors are detected in non-signaling portions of a frame, the entire frame is discarded.
FIG. 1 shows the format of a frame 100 transmitted over the Dedicated Control Channel/Fundamental Channel (DCCH/FCH). As specified in TIA/EIA/IS2000.2-A, the frame consists of Mixed Mode/Frame Mode (MM/FM) bits or Mixed Mode/Traffic Type/Traffic Mode (MM/TT/TM) bits, bearer bits, signaling bits, an outer CRC and tail bits. The signaling bits consist of a signaling message containing start of message (SOM) bits, message length, message body and an inner CRC. In current systems, a rate determination algorithm running in the BTS checks the outer CRC to determine whether a frame erasure has occurred. When the outer CRC indicates a corrupted frame, the entire frame is erased. As shown in FIG. 1, when there are no bits errors in the signaling message portion of the frame, the signaling message will still be erased based on the outer CRC check. This loss of signaling information can result in decreased system performance due to increased call setup time caused by increased retransmissions and reduced handoff success.
Thus, there is a need for an improved apparatus and method for processing a corrupted frame.